Added support for null geometries for to_file and from_file functions

- Closes-Bug: #138

examples/null_geom.geojson

@@ -0,0 +1,9 @@
+{
+"type": "FeatureCollection",
+"crs": { "type": "name", "properties": { "name": "urn:ogc:def:crs:OGC:1.3:CRS84" } },
+                                                                                
+"features": [
+{ "type": "Feature", "properties": { "Name": "Null Geometry" }, "geometry": null },
+{ "type": "Feature", "properties": { "Name": "SF to NY" }, "geometry": { "type": "LineString", "coordinates": [ [ -122.4051293283311, 37.786780113640894 ], [ -73.859832357849271, 40.487594916296196 ] ] } }
+]
+}

geopandas/geodataframe.py

@@ -68,7 +68,6 @@ class GeoDataFrame(GeoPandasBase, DataFrame):
         if not isinstance(col, (list, np.ndarray, Series)):
             raise ValueError("Must use a list-like to set the geometry"
                              " property")
-
         self.set_geometry(col, inplace=True)
 
     geometry = property(fget=_get_geometry, fset=_set_geometry,
@@ -177,7 +176,7 @@ class GeoDataFrame(GeoPandasBase, DataFrame):
             else:
                 f = f
 
-            d = {'geometry': shape(f['geometry'])}
+            d = {'geometry': shape(f['geometry']) if f['geometry'] else None}
             d.update(f['properties'])
             rows.append(d)
         df = GeoDataFrame.from_dict(rows)
@@ -326,8 +325,8 @@ class GeoDataFrame(GeoPandasBase, DataFrame):
                 'type': 'Feature',
                 'properties':
                     dict((k, v) for k, v in iteritems(row) if k != 'geometry'),
-                'geometry': mapping(row['geometry'])}
-
+                'geometry': mapping(row['geometry']) if row['geometry']
+                    else None}
         properties = OrderedDict([(col, convert_type(_type)) for col, _type
             in zip(self.columns, self.dtypes) if col != 'geometry'])
         # Need to check geom_types before we write to file...
@@ -335,7 +334,7 @@ class GeoDataFrame(GeoPandasBase, DataFrame):
         # Point, LineString, or Polygon
         geom_types = self['geometry'].geom_type.unique()
         from os.path import commonprefix # To find longest common prefix
-        geom_type = commonprefix([g[::-1] for g in geom_types])[::-1]  # Reverse
+        geom_type = commonprefix([g[::-1] for g in geom_types if g])[::-1]
         if geom_type == '': # No common suffix = mixed geometry types
             raise ValueError("Geometry column cannot contains mutiple "
                              "geometry types when writing to file.")

tests/test_geodataframe.py

@@ -30,6 +30,8 @@ class TestDataFrame(unittest.TestCase):
         self.df2 = GeoDataFrame([
             {'geometry': Point(x, y), 'value1': x + y, 'value2': x * y}
             for x, y in zip(range(N), range(N))], crs=self.crs)
+        self.df3 = read_file('examples/null_geom.geojson')
+        self.line_paths = self.df3['Name']
 
     def tearDown(self):
         shutil.rmtree(self.tempdir)
@@ -290,12 +292,21 @@ class TestDataFrame(unittest.TestCase):
         """ Test to_file and from_file """
         tempfilename = os.path.join(self.tempdir, 'boros.shp')
         self.df.to_file(tempfilename)
-        # Read layer back in?
+        # Read layer back in
         df = GeoDataFrame.from_file(tempfilename)
         self.assertTrue('geometry' in df)
         self.assertTrue(len(df) == 5)
         self.assertTrue(np.alltrue(df['BoroName'].values == self.boros))
 
+        # Write layer with null geometry out to file
+        tempfilename = os.path.join(self.tempdir, 'null_geom.shp')
+        self.df3.to_file(tempfilename)
+        # Read layer back in
+        df3 = GeoDataFrame.from_file(tempfilename)
+        self.assertTrue('geometry' in df3)
+        self.assertTrue(len(df3) == 2)
+        self.assertTrue(np.alltrue(df3['Name'].values == self.line_paths))
+
     def test_to_file_types(self):
         """ Test various integer type columns (GH#93) """
         tempfilename = os.path.join(self.tempdir, 'int.shp')